The present invention applies to chemical sensors, resonant sensors and eddy current instruments.
Recent efforts to provide a cleaner environment through reduction of point source and non point source pollution require the availability of chemical sensors to measure the presence and concentration of pollutants, including industrial gaseous emissions such as nitrous oxide, sulfur dioxide, hydrocarbons and liquid emissions such as nitrates, phosphates, ammonia-saturated liquids, chlorinated hydrocarbons and toxic materials.
Commercially available sensors for gaseous and liquid pollutants include ion selective electrodes (ISE's) and semiconductor potentiometric sensors with accuracy affected by numerous interfering agents. Furthermore, ISE's require the use of a reference electrode, may be fragile, respond slowly, are subject to fouling and require frequent calibration.
A resonant eddy-current instrument has been demonstrated to measure small changes in the conductivity of saline solutions caused by the growth of micro-organisms in a saline-based buffer. The change in resonance frequency with solution conductivity was found to be approximately 280 Hz per micro Siemens per centimeter indicating the range of instrument responses expected to five orders of magnitude changes in polymer conductivity.
Previous work in conductive polymer chemical sensors has relied upon the use of electrodes and electrode arrays for signal excitation and detection. Feasibility has been discussed for joining conductive polymer to a resonant metallic glass substrate for excitation by a radio-frequency electromagnetic wave. The use of a phthalonitrile conductive polymer resin as a reversible sensor for ammonia gas has been demonstrated. The intrinsic room temperature electrical conductivity of the phthalonitrile could be varied from 2 Siemens per meter to 20,000 Siemens per meter through suitable choice of the pyrolyzation temperature. The use of a polyaniline film based sensor in the detection of ammonia providing a 1585% change in conductivity upon exposure to ammonia gas has been shown.
Needs exist for chemical sensors which are precise, rugged, dependable, inexpensive and reliable.